METER TEROS 54 - Theory; Volumetric Water Content; Temperature

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TEROS 54
3.3 THEORY
The following sections explain the theory of VWC and temperature measured by TEROS54.
3.3.1 VOLUMETRIC WATER CONTENT
TEROS 54 sensors use an electromagnetic field to measure the dielectric permittivity of the
surrounding medium. The sensors supply a 70 MHz oscillating wave that charges according
to the dielectric of the material. The charge time is proportional to substrate dielectric and
substrate VWC. The TEROS 54 microprocessor measures the charge time and outputs a raw
value based on the substrate dielectric permittivity. The raw value is then converted to VWC
by a calibration equation specific to the substrate.
3.3.2 TEMPERATURE
The TEROS 54 uses four temperature sensors mounted on the PCB near the VWC sensors.
TEROS 54 temperature measurement is optimized to be accurate when the TEROS 54 is
buried in soil or substrate.
The TEROS 54 temperature output is in degrees Celsius unless otherwise stated in the data
logger program, such as in preferences in the ZENTRA Utility software.